Cutting Insert Having Cylindrically Shaped Side Surface Portions

ABSTRACT

A double-sided reversible and indexable cutting insert has identical opposing first and second end faces and a peripheral side surface extending therebetween. A clamping through-bore extends between, and opens out to, the first and second end faces. The cutting insert has a median plane between the first and second end faces, and a through-bore axis extending perpendicularly through the median plane. The cutting insert also has a Y-fold rotational symmetry about the through-bore axis. The peripheral side surface has Y major side surfaces and Y minor side surfaces, each minor side surface interconnecting two adjacent major side surfaces. Each minor side surface is a section of a single cylindrical surface having a given radius, the given radius being greater than a minor side surface distance of each minor side surface from the through-bore axis.

FIELD OF THE INVENTION

The present invention relates to a double-sided, indexable andreversible cutting insert for metal cutting operations, in general, andfor 45° shoulder face-milling operations, in particular.

BACKGROUND OF THE INVENTION

Such cutting inserts are generally provided with curved corners. U.S.Pat. No. 6,196,771 discloses a cutting insert having first and secondside faces. Each side face includes a pair of minor cutting edges ateach corner of the insert. The two minor cutting edges are located ontwo opposing sides of a corner bisector B, together forming an obtuseinner angle of about 170°, and are mirror-imaged about the bisector B.Two major cutting edges intersect respective ones of the minor cuttingedges whereby each major cutting edge and its associated minor cuttingedge together form a cooperating pair of cutting edges. There are twosuch cooperating pairs at each corner of each side face, whereby theinsert has at least sixteen cooperating pairs. During a millingoperation the insert is oriented so that only one cutting corner engagesa work-piece, and only one of the cooperating pairs of cutting edges ofthat cutting corner is operative. Only half of the major cutting edge ofeach cooperating pair is effective. The minor cutting edge of theoperative cooperating pair of cutting edges constitutes a wiper edge, bybeing arranged parallel to the surface of the work-piece, that isperpendicularly to an axis of rotation of a milling tool in which thecutting insert is mounted.

A drawback of these known inserts is that the minor cutting edge of eachcooperating pair has a constant setting angle during the machining ofthe work-piece. Positioning deviation of the cutting insert relative toa cutter body of a milling cutter in which the cutting inserts aremounted, or axial bending of the milling cutter (which may occur underdemanding machining conditions) may result in either a wiper corneradjacent the main cutting edge, or a wiper corner distal the maincutting edge of the cooperating pair cutting into the work-piece face,and thereby marring the face of a work-piece being milled.

U.S. Pat. No. 5,032,049 discloses an indexable cutting insert for facemilling of engine blocks of cast iron. The insert has two opposing,substantially identical, generally square-shaped upper and lowersurfaces which are perpendicularly connected by four side surfaces. Twoadjacent side surfaces connect to each other via a smoothly roundedcorner. The radius of the corner R is ¼ to ⅛ of a length X of theinsert, and therefore the setting angle gets close to zero degreesduring machining of the engine block when the insert gets close to theborder line of the work piece. The corner of the cutting insert servesin machining the shoulder of a work-piece, as well as in finishing theface of the work-piece during the last pass of the milling cutter.

It is an object of the present invention to provide an improved cuttinginsert. This object is attained with the subject matter in accordancewith the claims.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided adouble-sided reversible and indexable cutting insert comprisingidentical opposing first and second end faces and a peripheral sidesurface extending therebetween. A clamping through-bore extends between,and opens out to, the first and second end faces. The cutting insert hasa median plane extending between the first and second end faces and athrough-bore axis extending perpendicularly through the median plane.The cutting insert has a Y-fold rotational symmetry about thethrough-bore axis. The peripheral side surface comprises Y major sidesurfaces and Y minor side surfaces, each minor side surfacesinterconnecting two adjacent major side surfaces. Each minor sidesurface is a section of a single cylindrical surface having a givenradius; the given radius is greater than a minor side surface distanceof each minor side surface from the through-bore axis.

Preferably, each minor side surface has an associated minor surface axisextending parallel to the through-bore axis.

Further preferably, in an end view of the cutting insert, the minor sidesurface subtends a minor central angle of less than 15°.

Yet further preferably, the minor central angle is less than 5°.

Generally, the peripheral side surface meets the first and second endfaces each at a continuous peripheral edge. Each peripheral edgecomprises Y major edges and Y minor edges. Each major edge is formed atan intersection of an associated major side surface and a respective oneof the first and second end faces. Each minor edge is formed at anintersection of an associated minor side surface and a respective one ofthe first and second end faces, and interconnects two adjacent majoredges. If desired, each minor edge extends between a raised corner,formed at a meeting of the minor edge with a preceding major edge, and alowered corner, formed at a meeting of the minor edge with a followingmajor edge. The raised corner is disposed farther from the median planeM than the lowered corner.

If further desired, the through-hole axis and the minor side surfaceaxis define a bisector plane bisecting the minor side surface. Thebisector plane and the median plane define a minor axis about which theminor side surface has 180° rotational symmetry.

Generally, two adjacent major median lines formed at intersections ofthe median plane with each of two adjacent major side surfaces,respectively, meet at an apex located on the minor axis of the minorside surface interconnecting the two adjacent major side surfaces.

Typically, the median plane intersects each minor side surface at aminor median line.

Preferably, each major median line is a straight line.

Further preferably, the minor axis bisects an internal major angledefined by the two adjacent major median lines.

If desired, each major side surface comprises a median surface extendingtransversely away from a major median line formed at an intersection ofthe median plane with the major surface, towards the first and secondmajor edges.

If further desired, each major side surfaces comprises first and secondsupport surfaces extending from the median surface towards therespective one of the first and second end faces.

If yet further desired, each major side surfaces comprises first andsecond primary relief surface extending transversely the major edgeadjacent the respective one of the first and second end faces towardsthe support surface.

Preferably, the first and second support surfaces form each an acuteinternal support angle with the median plane, the first and secondrelief surface form each an acute internal relief angle with the medianplane, and the internal support angle is equal to, or greater than, theinternal relief angle.

Further preferably, the internal relief angle is largest adjacent thelower corner and smallest adjacent the raised corner of the major edge.

Generally, the minor side surface is perpendicular to the median plane.

If desired, in a major side view of the cutting insert, a major sideline parallel to the major median line and passing through the loweredcorner is longer than the major median line. If further desired, in aminor side view of the cutting insert, a minor side line parallel to theminor median line and passing through the lowered corner is shorter thanthe minor median line.

The present invention provides the following preferred advantages:

Because the entire length of each minor edge constitutes a wiper edge,positional deviation of the cutting insert in the insert pocket may notlead to reduced cutting performances, so that the wiper edge may be ableto continue machining the work-piece face, substantially withoutcompromising the smoothness of the work-piece face and to the quality ofthe finished product;

Peripheral surfaces of cutting inserts are often ground to reducepositioning deviation and to achieve a high quality finished product;however, the cutting insert of the present invention is capable ofreducing the effects of positional deviation without necessitatinggrinding of the peripheral side surface.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention and to show how thesame may be carried out in practice, reference will now be made to theaccompanying drawings, in which:

FIG. 1 shows a perspective view of a milling cutter having a cuttinginsert in accordance with the present invention mounted therein;

FIG. 2 shows a perspective view of the cutting insert shown in FIG. 1;

FIG. 3 shows a top view of the cutting insert shown in FIG. 2;

FIG. 4 shows a major side view of the cutting insert shown in FIG. 2;

FIG. 5 shows a minor side view of the cutting insert shown in FIG. 2;

FIG. 6 shows a section view of the cutting insert, taken along the lineVI-VI in FIG. 2;

FIG. 7 shows a section view of the cutting insert, taken along the lineVII-VII in FIG. 2;

FIG. 8 shows a section view of the cutting insert, taken along the lineVIII-VIII in FIG. 2;

FIG. 9 shows a perspective view of an insert pocket of the millingcutter shown in FIG. 1;

FIG. 10 shows a front view of the of the milling cutter shown in FIG. 1;

FIG. 11 shows a front view of the of the milling cutter shown in FIG. 1;

FIG. 12 shows a radial side view of the of the milling cutter shown inFIG. 1, taken perpendicularly to the radial plane P in FIG. 10; FIG. 13shows a detail view showing a wiper edge of the cutting insert mountedin a correct position in the insert pocket of the cutter tool shown inFIG. 11;

FIG. 14 shows a detail view of the wiper edge of the cutting insertshown in FIG. 13, mounted in a deviated position.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Attention is first drawn to FIG. 1. A cutting insert 20 in accordancewith the present invention is secured to a cutter body 22 of a rotarymilling cutter 24 by a clamping screw 26. The cutting insert 20 is of adouble-sided, indexable and reversible type, and is generally adapted toperform face—and 45° shoulder-milling a work-piece (not shown).

Attention is now drawn to FIGS. 2 to 5. The cutting insert 20 hasidentical and opposing first and second end faces 28, 30. In an end viewof the cutting insert 20, best shown in FIG. 3, each of the identicalfirst and second end faces 28, 30 is of a general form of a squarehaving curved corners. A peripheral side surface 32 extends between theopposing first and second end faces 28, 30. The cutting insert is of anegative type and therefore the peripheral side surface 32 is generallyperpendicular to both end faces 28, 30. The peripheral side surface 32has four identical major side surfaces 34 of a generallyparallelogrammatic shape, and four identical minor side surfaces 36,also of a general parallelogrammatic shape. Each minor side surface 36interconnects two adjacent major side surfaces 34.

A given major side surface 34 has 180° rotational symmetry about givenmajor axis I associated therewith and extending generallyperpendicularly therethrough. Similarly, a given minor side surfaces 36has 180° rotational symmetry about given minor axis J associatedtherewith and passing generally perpendicularly therethrough. The majorand minor axes I, J are co-planar and intersect at an insert center C todefine an insert median plane M. A given major axis I defines an axisangle α of 45° with a given minor axes J.

The cutting insert 20 is provided with a clamping through-bore 38extending between, and opening out to, the first and second end faces28, 30. The clamping through-bore 38 is adapted for receiving theclamping screw 26. The clamping through-bore 38 has a through-bore axisT extending perpendicularly to the median plane M through the insertcenter C, so that the first and second end faces 28, 30 each have 90°rotational symmetry about the through-bore axis T. The first and secondend faces 28, 30 have each four raised corners 40 and four loweredcorners 42. The raised corners 40 of each of the first and second endfaces 28, 30 lie in a first and second end planes E_(F), E_(S),respectively. The median plane M is parallel to, and lies midwaybetween, the first and second end planes E_(F), E_(S). The loweredcorners 42 are closer to the median plane M than the raised corners 40.

The major and minor side surfaces 34, 38 are each intersected by themedian plane M to form major and minor median lines L_(I), L_(J),respectively. As best shown in FIG. 4, a major side lines S_(I) lying onthe major side surface 34 and extending from the lowered corner 42parallel to the major median line L_(I) is longer than the major medianline L_(I). As best shown in FIG. 5, a minor side lines S_(J) lying onthe minor side surface and extending from the lowered corners 42parallel to the minor median line L_(J) is shorter than the minor medianline L_(J).

As is best shown in FIG. 3, imaginary extensions of the major medianlines L_(I)′, L_(I)″ of two adjacent major side surfaces 34 meet at anapex A to define an internal corner angle μ. The apex A lies on theminor axis J associated with the minor side surface 36 extending betweenthe adjacent major side surfaces 34. In a particular embodiment, thecorner angle μ is a right angle. A bisector plane B passes through thethrough-bore axis T and the respective minor axis J extendingperpendicularly to the median plane M to bisect the corner angle μ.

Each minor side surface 36 is a section of a single cylindrical surfaceextending transversely to the median plane M. Each minor side surface 36has a minor surface radius R extending thereto from an associated minorsurface axis N lying in the associated bisector plane B parallel to thethrough-bore axis T. The minor side surface 36 intersects the associatedminor axis J at a minor surface distance D from the insert center C.Generally, the minor surface radius R is two to twelve times as large asthe minor surface distance D and more preferably is between three to sixtimes as large. In the particular embodiment shown, the minor surfaceradius R is approximately four times greater than the minor surfacedistance D. The minor side surfaces do not all have to conform to thesame cylindrical surface. The minor side surface 36 subtends an acuteminor central angle ν, preferably of less than 15°. In a non-bindingexample, the minor central angle ν is approximately 4° 30′.

The first and second end faces 28, 30 each intersect the peripheral sidesurface 32 at a peripheral edge 44. The peripheral edges 44 have eachfour major edges 46 associated with the adjacent major side surface 34,and four minor edges 48 associated with the adjacent minor side surface.In the embodiment shown, a given major edge 46 extends between givenlowered corner 42 and given raised corner 40, and a given minor edgeextends between given raised corner 40 and given lowered corner 42. Eachof the major and minor edges 46, 48 may constitute major and minorcutting edges, respectively. The particular embodiment has four majorcutting edges and four minor cutting edges associated with each of thefirst and second end faces 28, 30, for a total of eight major and eightminor cutting edges.

The first and second end faces 28, 30 have each a peripheral rakesurface 50 extending in an inward direction of the cutting insert fromthe respective peripheral edge 44 towards an end abutment surface 52.The end abutment surfaces 52 may be generally flat, and substantiallyparallel to each other and to the median plane M. In an end view of thecutting insert, the end abutment surfaces 52 has a general form of asquare having beveled corners, which is rotated relatively to therespective end face 28, 30. The peripheral rake surfaces 50 compriseeach four major rake surfaces 54 associated with the major edges 46 andfour minor rake surfaces 56 associated with the minor edges 48. Themajor and minor rake surfaces 54, 56 have major and minor rake widthsW_(I), W_(J), respectively, defined in directions transverse to theassociated major and minor edges 46, 48, respectively. The major rakewidth W_(I) increases from a minimal major rake width adjacent thelowered corner 42 to a maximal major rake width adjacent the raisedcorner 40 of the respective major edge 46, while the minor rake widthW_(J) decreases from a maximal minor rake width adjacent the raisedcorner 40 to a minimal minor rake width adjacent the lowered corner 42of the respective minor edge 48.

Peripheral rake steps 58 are formed between the peripheral rake surfaces50 and the respective end abutment surface 52. The rake step 58 extendsfrom the end abutment surface 52 transversely to the median plane M to astep height H_(S) (see FIG. 6). The step height H_(S) increasesgradually from a minimal step height adjacent the lowered corner 42 to amaximal step height adjacent the raised corner 40. In the particularembodiment, the minimal step height is zero.

As seen in FIG. 6, the major side surfaces 34 comprise each first andsecond primary relief surfaces 62, 64 adjacent each of the first andsecond end surfaces 28, 30, respectively. Each of the first and secondprimary relief surfaces 62, 64 extends from the adjacent major edge 46towards the major median line L_(I). First and second side abutmentsurfaces 66, 68 extend along each major side surface 34 away from thefirst and second primary relief surfaces 62, 64, respectively, towards asubstantially planar side median surface 70 extending therebetweengenerally perpendicularly to the median plane M.

As seen in FIGS. 6 and 7, in each major cross section of the cuttinginsert, taken in a plane generally perpendicular to a given major sidesurface 34, the first and second primary relief surfaces 62, 64 may bestraight, or they may be convexly curved. The major rake surfaces 54 maybe straight, or they may be concavely curved. First and second primaryrelief lines F_(F), F_(S) tangent to the first and second primary reliefsurfaces 62, 64, respectively, at the respective major edge 46 form eachan acute interior relief angle φ with the median plane M. The reliefangle φ may be constant or may vary along the major edge. The variationof the relief angle φ may be in accordance to any desired definition.The first and second side abutment surfaces 66, 68 form each an acuteside abutment angle α with the median plane M. The side abutment angle αmay be generally constant along the major side surface 34, and isgenerally equal to, or greater than, the relief angle φ. In theparticular embodiment, the primary relief angle φ is equal to the sideabutment angle a adjacent the lower corner 42, and decreases along themajor edge 46 towards the raised corner 40 in such a way so as to definea helically twisting primary relief surface 62, 64. As is best shown inFIG. 8, in each minor cross section of the cutting insert 20, taken in aplane generally perpendicular to a given minor side surface 36, theminor side surface 36 is perpendicular to the median plane M.

Attention is now drawn to FIGS. 9 to 12. The milling cutter 24 isrotatable about an axis of rotation X defining a front-to-rear directionand a direction of rotation Z, and has four cutting inserts 20 inaccordance with the present invention mounted each in an insert pocket72 provided at a cutter front end 74 of the cutter body 22. It should benoted that directional terms appearing throughout the specification andclaims, e.g. “front”“rear”etc., (and derivatives thereof) are forillustrative purposes only, and are not intended to limit the scope ofthe appended claims. The insert pocket 72 comprises adjacent inner andouter walls 76, 78, generally transverse to a pocket base 80. The outerwall 78 is provided with an outer location surface 82 and the inner wall76 is provided with spaced apart front and rear location surfaces 84, 86located on either side of a central recessed region 88 of the inner wall76. The pocket base 80 is provided with a threaded bore 90 for receivingthe clamping screw 26 in order to secure the cutting insert 20 in theinsert pocket 72.

When the cutting insert 20 is secured in the insert pocket 72, one ofthe first and second end faces 28, 30, e.g., the first end face 28, ispositioned to face generally tangentially forwardly in the direction ofrotation Z of the milling cutter, and constitutes an operative end face92. The second end face 30 constitutes a supporting end face (notshown), and is positioned with the respective end abutment surface 52abutting the pocket base 80. A front outer major edge 96 of theoperative end face 92 constitutes an operative major cutting edge 98,while a front minor edge 100 of the operative end face 92 constitutes anoperative minor cutting edge 102 associated with the operative majorcutting edge 98. The first side abutment surface 66 of an inner rearmajor side surface (not shown), located adjacent the operative end face92 and opposite the operative major cutting edge 98, abuts the front andrear location surfaces 84, 86. The first side abutment surface 66 of anouter rear major side surface (not shown) located adjacent the operativeend face 92 and adjacent the operative major cutting edge 98 abuts theouter location surface 82 of the insert pocket 72.

The cutting insert 20 and the milling cutter 24 shown in the figures maybe used to face-mill a work-piece (not shown), machining a 45° shoulderon the work-piece face, and therefore the cutting insert 20 is locatedin the insert pocket 72 so that, when the milling cutter 24 is rotatedabout the axis of rotation X, the operative major cutting edge 98describes a frustoconical envelope having a generator line G forming agenerator angle γ of generally 45° with the axis of rotation X. In orderto provide a high-quality work-piece face relatively free from machiningmarks or blemishes, the operative minor cutting edge 102 functions as awiper edge 106. The wiper edge 106 is adapted to machine a substantiallyflat face on the work-piece at 90° to the axis of rotation X of themilling cutter 24. The operative major cutting edge 98 forms a positivemajor axial rake angle γA with a radial plane P passing through a raisedcorner 40 thereof and through the axis of rotation X of the millingcutter 24 (best shown in FIG. 12).

The cutting insert 20 shown in the figures may be indexed in the insertpocket 72 about its through-hole axis T in four steps of 90°, eachindexing step positioning a fresh major edge 46 as the operative majorcutting edge 98. The cutting insert 20 may additionally be reversed sothat the first end face 28 may become the supportive end face (notshown) and the second end face 30 may become the operative end face 92,providing four additional fresh major edges 46 which can be indexed tothe position of the operative major cutting edge 98. Generally, each ofthe major and minor edges 46, 48 constitutes “full effective” cuttingedges, i.e., the entire extent of each of the major and minor edges iscapable of performing machining operations in a given position of thecutting insert 20.

The cutting insert 20 in accordance with the present invention ispreferably manufactured by form-pressing or injection molding andsintering of metallurgical, ceramic or cermet powders. The peripheralside surface 32 of the cutting insert 20 may be ground to increasepositioning accuracy thereof in the insert pocket 72, which may bedesirable in milling a smooth, high-quality face of the work-piece.However, in accordance with the present invention, it may not benecessary to grind the peripheral side surfaces 32 while maintainingdesired smoothness and quality of the milled face of the work-piece.

Attention is directed to FIGS. 13 and 14, showing the cutting insert inaccordance with the present invention machining the work-piece face 108while being secured in the milling cutter in a correct position (FIG.13) and in a deviated position (FIG. 14). In the correct position (FIG.13), the wiper edge 106 of the cutting insert machines the work-pieceface 108 at a first wiping region K1 located on a first wiper portion110 extending between the bisector plane B and the associated operativemajor cutting edge 98. However, even when mounted in the deviatedposition (FIG. 14), the wiper edge 106 still machines the work-pieceface 108, albeit at a second wiping region K2 located on a second wiperportion 112 extending from the bisector plane B away from the operativemajor cutting edge 98.

Although the present invention has been described to a certain degree ofparticularity, it should be understood that various alterations andmodifications could be made without departing from the spirit or scopeof the invention as hereinafter claimed.

1. A double-sided reversible and indexable cutting insert comprising:identical opposing first and second end faces; a peripheral side surfaceextending between said first and second end faces, the peripheral sidesurface comprising Y major side surfaces and Y minor side surfaces, Ybeing an integer number, each minor side surface interconnecting twoadjacent major side surfaces; a clamping through-bore extending between,and opening out to, the first and second end faces; a median plane (M)located between, and spaced apart from, the first and second end faces;and a through-bore axis (T) extending perpendicularly through the medianplane, with the cutting insert having Y-fold rotational symmetry aboutthe through-bore axis; wherein: each minor side surface is a section ofa single cylindrical surface having a radius (R), the radius (R) beinggreater than a minor side surface distance (D) between said each minorside surface and the through-bore axis.
 2. The cutting insert of claim1, wherein each minor side surface has an associated minor surface axis(N) extending parallel to the through-bore axis (T).
 3. The cuttinginsert of claim 1, wherein the radius (R) is between two and twelvetimes as large as the minor side surface distance (D).
 4. The cuttinginsert of claim 3, wherein the radius (R) is between three and six timesas large as the minor side surface distance (D).
 5. The cutting insertof claim 1, wherein in an end view of the cutting insert, the minor sidesurface subtends a minor central angle of less than 15°.
 6. The cuttinginsert of claim 5, wherein the minor central angle is less than 5°. 7.The cutting insert of claim 1, wherein: the peripheral side surfacemeets each of the first and second end faces at a peripheral edge; eachperipheral edge comprises Y major edges and Y minor edges; each majoredge is formed at an intersection of an associated major side surfaceand a respective one of the first and second end faces; and each minoredge is formed at an intersection of an associated minor side surfaceand a respective one of the first and second end faces, andinterconnects two adjacent major edges.
 8. The cutting insert of claim7, wherein: each minor edge extends between a raised corner formed at ameeting of the minor edge with a preceding major edge, and a loweredcorner formed at a meeting of the minor edge with a following majoredge; and the raised corner is disposed farther from the median plane Mthan the lowered corner.
 9. The cutting insert of claim 1, wherein: eachminor side surface has 180° rotational symmetry around a minor axis (J)that passes perpendicularly through said each minor side surface; andthe through-bore axis (T) and the minor axis (J) define a bisector plane(B) which bisects said each minor side surface.
 10. The cutting insertof claim 9, wherein two adjacent major median lines formed atintersections of the median plane with each of two adjacent major sidesurfaces, respectively, meet at an apex located on the minor axis (J) ofthe minor side surface interconnecting the two adjacent major sidesurfaces.
 11. The cutting insert of claim 10, wherein each major medianline is a straight line.
 12. The cutting insert of claim 11, wherein theminor axis bisects an internal major angle defined by the two straight,adjacent major median lines.
 13. The cutting insert of claim 1, whereineach major side surface comprises a median surface extending in oppositedirections away from a major median line formed at an intersection ofthe median plane with that major surface, towards first and second majoredges formed at the intersection of that major surface with respectivefirst and second end faces.
 14. The cutting insert of claim 13, whereinsaid each major side surface comprises first and second support surfacesextending from the median surface towards the first and second majoredges, respectively.
 15. The cutting insert of claim 14, wherein saideach major side surface comprises first and second primary reliefsurfaces extending from said first and second major edges towards thefirst and second support surfaces, respectively.
 16. The cutting insertof claim 15, wherein: the first and second support surfaces each form anacute internal support angle with the median plane; the first and secondprimary relief surfaces each form an acute internal relief angle withthe median plane; and the internal support angle is equal to, or greaterthan, the internal relief angle.
 17. The cutting insert of claim 15,wherein: each end face has Y raised corners and Y lowered corners, thelowered corners being closer to the median plane than the raisedcorners; each major edge extends between a lowered corner and a raisedcorner; the first and second primary relief surfaces each form an acuteinternal relief angle with the median plane; and the internal reliefangle is largest adjacent the lowered corner and smallest adjacent theraised corner of said each major edge.
 18. The cutting insert of claim1, wherein the minor side surface is perpendicular to the median plane.19. The cutting insert of claim 1, wherein: each end face has Y raisedcorners and Y lowered corners, the lowered corners being closer to themedian plane than the raised corners; each major side surface intersectsthe first and second end faces to form first and second major edges,respectively; each major edge extends between a lowered corner and araised corner; said each major side surface has a major median lineformed at an intersection of the median plane with that major sidesurface; and in a major side view of the cutting insert, a major sideline parallel to the major median line and passing through the loweredcorner is longer than the major median line.
 20. The cutting insert ofclaim 19, wherein each minor side surface intersects the first andsecond end faces to form first and second minor edges, respectively;each minor edge extends between a raised corner and a lowered corner;said each minor side surface has a minor median line formed at anintersection of the median plane with that minor side surface; and in aminor side view of the cutting insert, a minor side line parallel to theminor median line and passing through the lowered corner is shorter thanthe minor median line.
 21. The cutting insert of claim 1, wherein eachend face has Y raised corners and Y lowered corners, the lowered cornersbeing closer to the median plane than the raised corners; each minorside surface intersects the first and second end faces to form first andsecond minor edges, respectively; each minor edge extends between araised corner and a lowered corner; said each minor side surface has aminor median line formed at an intersection of the median plane withthat minor side surface; and in a minor side view of the cutting insert,a minor side line parallel to the minor median line and passing throughthe lowered corner is shorter than the minor median line.